I. Field of the Invention
The present invention relates to a process for growing a layer of high quality silicon dioxide on the surface of a silicon substrate at a relatively low temperature by illuminating the substrate with a broad spectrum of visible and infrared light in a substantially pure oxygen atmosphere.
II. Description of the Prior Art
Thin films of silicon dioxide are used extensively in a myriad of electronic devices exemplified by metal oxide semiconductors (MOS) and photovoltaic devices including solar cells and optical detectors. A silicon dioxide film functions not only as an insulator, but also as a surface passivating medium. Substantially all high efficiency solar cells use a thin layer of silicon dioxide to minimize surface recombination. It is therefore evident that silicon dioxide is an extremely important component of electronic devices.
Currently, there is considerable interest in reducing the thickness of silicon dioxide films to a range of 100.ANG.-300.ANG.. However, there have been difficulties in obtaining high quality, thin silicon dioxide films by conventional wet or dry oxidation. A typical current method for growing silicon dioxide by oxidation is employment of a thermal furnace wherein the silicon dioxide is produced on the substrate at temperatures of 850.degree. C. to 1,000.degree. C. and higher. In addition to being quite energy-inefficient, such a high-temperature furnace process requires utmost cleanliness of the furnace chamber, a requirement that many times is difficult to maintain.
Recently there has been considerable interest in using rapid thermal annealing (RTA) processes for deposition of thin silicon oxide film on silicon substrates. A popular approach is to use N.sub.2 O and silane for this purpose. Typically, these films are deposited at about 850.degree. C. Silicon dioxide films have also been grown by RTA processes at conventional furnace temperatures as recited above, with the results being similar to conventional furnace-produced oxides.
Other prior art methods typically employ a chemical vapor deposition process in combination with ultraviolet radiation, such as from a mercury lamp, to deposit an oxide on a substrate. The radiation is an energy source which dissociates constituent reactants such as silane, N.sub.2 O, etc. in the ambient to produce favorable reactions that produce the desired oxide for deposition.
In view of the above-described approaches for the production of silicon dioxide, it is apparent that a need is present for silicon dioxide production on a silicon substrate wherein such production is accomplished in a straight forward manner at a relatively low temperature with high-quality yields. Accordingly, a primary object of the present invention is to provide a process for producing a layer of silicon dioxide on a silicon substrate using optical processing wherein the substrate itself is the source of the silicon component of the silicon dioxide so produced.
Another object of the present invention is to provide a method for producing the layer of silicon dioxide by using a broad spectrum of visible and infrared light to illuminate the silicon substrate, with such optical energy being the sole heat source for reactivity.
Yet another object of the present invention is to provide a method for producing the silicon dioxide layer whereby reactivity occurs in an oxygen atmosphere such that silicon of the silicon substrate itself is consumed to thereby produce a silicon dioxide layer on the substrate.
These and other objects of the present invention will become apparent throughout the description of the invention which now follows.